Really hard to tell without seeing how different the two designs are and not knowing what's the TOS of the original post. So you're saying that the design is suppose to be a 100% one-off but the artist recolored the base and sold it to the 2nd highest bidder?

If the design was unique, something about it like the anatomy, that these elements as a whole design are suppose to be a one-off, then yes, a beware is well warranted regardless if the base was re-colored or even if lines or pose were redone.

I think the 2nd owner should either be refunded or be given a new design.